The present invention relates to phosphorescent organic electroluminescent devices which comprise fluorene and spirobifluorene derivatives as matrix materials.
Organic semiconductors are being developed for a number of electronic applications of different types. The structure of organic electroluminescent devices (OLEDs) in which these organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. No. 4,539,507, U.S. Pat. No. 5,151,629, EP 0676461 and WO 98/27136. However, further improvements are still necessary. Thus, there is still a need for improvement, in particular with respect to the lifetime, efficiency and operating voltage of organic electroluminescent devices. It is furthermore necessary for the compounds to have high thermal stability and a high glass-transition temperature and to be capable of sublimation without decomposition.
Especially in the case of phosphorescent electroluminescent devices, improvements in the above-mentioned properties are still necessary. In particular, there is a need for improvement in the case of matrix materials for phosphorescent emitters which simultaneously result in good efficiency, a long lifetime and a low operating voltage. These very properties of the matrix materials are frequently limiting for the lifetime and efficiency of the organic electroluminescent device.
In accordance with the prior art, carbazole derivatives, for example bis-(carbazolyl)biphenyl, are frequently used as matrix materials. There is still a need for improvement here, in particular with respect to the lifetime and glass-transition temperature of the materials.
Furthermore, ketones (WO 04/093207), phosphine oxides and sulfones (WO 05/003253) are used as matrix materials for phosphorescent emitters. Low operating voltages and long lifetimes are achieved, in particular, with ketones. There is still a need for improvement here, in particular with respect to the efficiency and compatibility with metal complexes which contain ketoketonate ligands, for example acetylacetonate.
Furthermore, metal complexes, for example BAlq or bis[2-(2-benzothiazole)phenolate]zinc(II), are used as matrix materials for phosphorescent emitters. There is still a need for improvement here, in particular with respect to the operating voltage and the chemical stability. Purely organic compounds are frequently more stable than these metal complexes. Thus, some of these metal complexes are hydrolysis-sensitive, which makes handling of the complexes more difficult.
In particular, there is still a need for improvement in the case of matrix materials for phosphorescent emitters which simultaneously result in high efficiencies, long lifetimes and low operating voltages and which are also compatible with phosphorescent emitters which carry ketoketonate ligands.
Surprisingly, it has been found that fluorene derivatives and corresponding heterocyclic derivatives which are substituted by triazine or other electron-deficient nitrogen heterocycles, in particular spirobifluorene derivatives, are very highly suitable as matrix materials for phosphorescent emitters and result, in this use, in OLEDs which simultaneously have high efficiencies, long lifetimes and low operating voltages, including with phosphorescent emitters which contain ketoketonate ligands.
U.S. Pat. No. 6,229,012 and U.S. Pat. No. 6,225,467 disclose the use of fluorene derivatives which are substituted by triazine groups as electron-transport material in OLEDs. However, the application does not reveal that these materials are also suitable as matrix materials for phosphorescent emitters.
WO 05/053055 discloses the use of triazine derivatives, in particular spirobifluorene derivatives, which are substituted by triazine groups as hole-blocking material in phosphorescent OLEDs. However, the application does not reveal that these materials are also suitable as matrix materials for phosphorescent emitters.